Silicon-on-insulator (SOI) technology, an important integrated circuit technology, deals with forming transistors in a layer of semiconductor material that overlies an insulating layer. A common embodiment of SOI structures is a single crystal layer or more of silicon that overlies a layer of silicon dioxide. High performance and high density integrated circuits are achievable using SOI technology, because of the reduced parasitic elements that are present in the integrated circuits that use SOI transistors.
Problems that exist with SOI transistor technology relates to polysilicon gate integrity. These problems exist in three areas. First of all, mesa-isolated SOI transistors have poor gate oxide integrity at the mesa edges due to thinning of the thermally grown gate oxide at the mesa edges. Secondly, mesa-isolated SOI transistors contain a parasitic MOSFET along the mesa sidewall whose conduction produces a high leakage currents in the SOI transistor. Another problem of known SOI transistors is that, due to the vertical topography of the SOI mesa, it is difficult to suppress the formation of polysilicon stringers along the bottom edge of the mesa during the polysilicon gate electrode anisotropic etching.